Welcome Opah to the Warm-Blooded Club

Welcome Opah, the new member of the warm-blooded club.

The scientists’ team from the NOAA SouthWest Fisheries Science Center in California discovered the first fully warm-blooded fish, Opah (otherwise known as the moonfish or Lampris Guttatus).

According to the report published in the journal Science the zoological curiosity is a long time acquaintance of fish markets and restaurant menus, but its distinguishing characteristics have been discovered only recently.

The NOAA team, led by Nicholas Wegner found that Opah has a warm heart and maintains a high body temperature that indicates a surprising evolutionary development. Until recently, it was believed that fish cannot maintain high body temperatures as they extract oxygen from the water through their gills.

While blood temperature can be raised momentarily by muscle activity, when it comes out of the heart it is transported to the gills to be cooled to ocean temperature.

The Opah presents an insulated network of blood vessels in-between its heart and its gills that acts as a heat exchanger. Warm blood pushed from the heart reheats the oxygenated blood from the gills before going to its body, thus retaining body heat.

An astonishing evolutionary development that allows the Opah to maintain a 5 degrees higher body temperature in the coldness of the deep sea. The fish swims 500 meters bellow the surface without being at risk to cool down due to the temperature of the surrounding water.

From this perspective the Opah is in a great advantage. It can move faster when hunting or avoiding peril. Also, being warm blooded allows the fish to stay deep underwater indefinitely as the layer of fat in the skin maintains the warmth of the heart, the brain and the vital organs.

The moonfish takes its name from its peculiar flattened disk shape. It displays bright rusty red fins with white spots. It has been reported that it reaches two meters in length and approximately 90 kilograms in weight. Except for polar seas, the Opah can be found swimming solitarily in all oceans. Here, it hunts squid for survival.

It hasn’t been established so far if this is an evolutionary trend for ocean fish. For those living in tropical seas, life conditions are ideal with regard to warm water temperature. But for fish living in the ocean, being warm-blooded, thus emulating mammals, represents a better chance for survival.

Image Source: Marine Creations